Nature utilizes self assembly to construct, as well as organize, well-defined biopolymers, such as DNA, RNA, and proteins. These biopolymers have inspired synthetic chemists to use the concept of self assembly and directed self assembly to create well-defined nanostructured materials. Advances in synthetic polymer chemistry have enabled the synthesis of polymers with defined molecular weight, composition, and low polydispersity. As a result of these advances, block copolymers have been identified as useful macromolecular tectons for self assembly. Block copolymers self assemble into a range of morphologies that enable their utility in a number of potential applications, such as lithography, composites, plastics, and low-k dielectrics. The ordered phases obtained by the block copolymers are largely dictated by the characteristics of the polymer, such as the polymer composition, the degree of polymerization of the polymer under certain conditions, and the effective segment-segment compatibility parameter (χ) of the polymer.
Among the first class of self-assembling block copolymers to be used for the preparation of porous dielectric materials were amphiphilic surfactants, such as cetyltrimethylammonium bromide (CTAB). Self-assembling block copolymers, such as pluronics, have also been investigated for the preparation of porous dielectric materials. Beyond porous dielectric materials, polystyrene/poly(ethylene oxide) (PS-PEO) block copolymers have been combined with inorganic precursors to generate inorganic nanostructures for patterning applications.
Currently used processes for generating silicate nanostructures from self-assembling block copolymers require the following: (1) co-assembling an organic component, such as a block copolymer, with an inorganic precursor such as tetraethoxysilane (TEOS) or a silsesquioxane polymer, such as methylsilsesquioxane (MSSQ); and (2) condensing the inorganic component to form a crosslinked silicate matrix. The crosslinked matrix can be further thermally treated to decompose the organic segments to form a nanoporous silicate.